Approach for controlling fuel flow with alternative fuels

ABSTRACT

Fuel is evacuated from a fuel rail by directing liquid fuel from the fuel rail to a fuel tank and then by directing gaseous fuel from the fuel rail to a fuel vapor canister.

BACKGROUND AND SUMMARY

In some internal combustion engine applications, liquid propaneinjection can provide some potential benefits relative to gaseouspropane injection in ether port fuel injection or direct fuel injectionsystems. As one example, liquid propane injection provides reduced airdisplacement that allows for increased air mass to enter an enginecylinder resulting in increased volumetric efficiency relative togaseous propane injection.

A typical liquid injection propane fuel system for an internalcombustion engine supplies liquid propane from a pressurized tank via afuel pump to a fuel rail. The liquid propane is injected from the fuelrail to cylinders of the internal combustion engine via fuel injectors.Excess fuel can be returned to the pressurized tank during operation viaa pressure relief supply line.

However, the inventor has recognized several potential issues with suchliquid propane fuel systems. For example, during engine shut-offconditions, fuel rail pressure is reduced so that propane cannot bepumped back to the fuel tank via the pressure relief supply line andinstead resides in the fuel rail. The liquid propane residing in thefuel rail during engine shut-off conditions may evaporate and leak outof the fuel rail via the fuel injectors into the atmosphere causingincreased emissions and reduced fuel economy.

In one example, the above mentioned issues may be addressed by a methodfor controlling fuel flow in a vehicle. The method may comprise during afirst mode of operation, directing fuel from a fuel rail to a fuel tank,and during a second mode of operation, directing fuel from the fuel railto a fuel vapor canister.

As an example, the first and second mode may be performed during avehicle shut-off condition in order to evacuate fuel from the fuel rail.By operating in the first mode, liquid fuel may be evacuated from thefuel rail and returned to the fuel tank. In particular, at vehicleshut-off a fuel rail pressure may be significantly higher than a fueltank pressure. This pressure difference forces liquid fuel from the fuelrail to the fuel tank. As the liquid fuel evacuates from the fuel rail,the remaining fuel evaporates into gaseous fuel causing a drop inpressure which stops evacuation of the liquid fuel. Accordingly, byoperating in the second mode, the remaining gaseous fuel can be directedto the fuel vapor canister. In this way, evaporative emissions resultingfrom fuel in the fuel rail evaporating and leaking out of the fuelinjectors can be reduced and fuel economy can be increased.

It will be understood that the summary above is provided to introduce insimplified form a selection of concepts that are further described inthe detailed description, which follows. It is not meant to identify keyor essential features of the claimed subject matter, the scope of whichis defined by the claims that follow the detailed description. Further,the claimed subject matter is not limited to implementations that solveany disadvantages noted above or in any part of this description.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the present disclosure will be better understoodfrom reading the following detailed description of non-limitingembodiments, with reference to the attached drawings, wherein:

FIG. 1 shows an embodiment a fuel system for an internal combustionengine including a single fuel rail evacuation stage including anejector.

FIG. 2 shows an embodiment of a fuel system for an internal combustionengine including a plurality of fuel rail evacuation stages that eachincludes an ejector.

FIG. 3 shows an embodiment of a multi-fuel system for an internalcombustion engine including a fuel rail evacuation stage including anejector.

FIG. 4 shows an embodiment of a fuel system for an internal combustionengine where liquid fuel and gaseous fuel are evacuated from a fuelrail.

FIG. 5 shows an embodiment of a fuel system for an internal combustionengine where a fuel pump temperature is controlled based on selectivefuel expansion.

FIG. 6 shows an embodiment of a method for controlling a fuel systemincluding one or more fuel rail evacuation stages.

FIG. 7 shows an embodiment of a method for controlling a multi-fuelsystem including one or more fuel rail evacuation stages.

FIG. 8 shows an embodiment of a method for evacuating liquid and gaseousfuel from a fuel rail.

FIG. 9 shows an embodiment of a method for controlling a fuel pumptemperature based on selective fuel expansion.

DETAILED DESCRIPTION

The present description relates to a fuel system for an internalcombustion engine of a vehicle. More particularly, the presentdescription relates to a fuel system that provides versatility so thatdifferent fuel types can be injected for combustion, if desired. Thefuel system is capable of evacuating the fuel rail upon vehicle shut-offto reduce emissions. Further, since the fuel rail is evacuated differentfuels can be selected for combustion upon start-up. For example, thefuel system may include an ejector to evacuate fuel from a fuel railduring an engine shut-off condition of the vehicle. During engineoperation, a fuel pump delivers fuel from a fuel tank to the fuel rail.On the other hand, during the engine shut-off condition, the fuel pumpprovides the motive flow for the ejector to evacuate fuel residing inthe fuel rail back into the fuel tank. In some embodiments, the fuelsystem may include a plurality of ejectors, connected in differentstages, to provide a lower evacuation pressure that further reduces fuelrail pressure so as to evacuate a greater amount of fuel from the fuelrail back to the fuel tank.

As another example, the fuel rail can be evacuated by leveraging apressure differential between the fuel rail and a fuel tank to push outliquid fuel from the fuel rail and direct it to the fuel tank.Subsequently, gaseous fuel remaining in the fuel rail can be directed toa fuel vapor canister to evacuate the fuel rail. Since the fuel rail isevacuated, the fuel system provides the ability to select a differenttype of fuel for combustion at start-up.

Furthermore, the fuel system may include a fuel pump that is temperaturecontrolled to accept different fuel types by selectively providingliquid fuel as a refrigerant to cool the fuel pump. In particular,liquid fuel can be selectively directed to an expansion section that isthermally connected to the fuel pump to cool the fuel pump to a suitabletemperature. Accordingly, pressure can be reduced to prevent a selectedfuel type from undergoing a liquid-to-gas phase change that wouldinhibit the fuel pump from pumping the liquid fuel.

The subject matter of the present description is now described by way ofexample and with reference to certain illustrated embodiments.Components that may be substantially the same in two or more embodimentsare identified coordinately and are described with minimal repetition.It will be noted, however, that components identified coordinately indifferent embodiments of the present description may be at least partlydifferent. It will be further noted that the drawings included in thisdescription are schematic. Views of the illustrated embodiments aregenerally not drawn to scale; aspect ratios, feature size, and numbersof features may be purposely distorted to make selected features orrelationships easier to see.

FIG. 1 schematically shows an engine system 100 that may be included ina propulsion system of an automobile or other vehicle. The engine system100 includes an internal combustion engine 102. The internal combustionengine 102 includes one or more cylinders 104 that may receive intakeair from an intake manifold (not shown) and/or fuel from one or morefuel injectors 106. The fuel injectors 106 may be arranged in an intakepassage in a configuration that provides what is known as port injectionof fuel into the intake port upstream of the cylinder 104. The fuelinjector 106 may inject fuel in proportion to a pulse width of a signalreceived from a controller 128 via an electronic driver (not shown).Fuel may be delivered to the fuel injector 106 from a fuel rail 108 by afuel system 110. In some embodiments, cylinder 104 may alternatively oradditionally include a fuel injector coupled directly to cylinder 104for injecting fuel directly therein, in a manner known as directinjection.

The fuel system 110 may include a fuel tank 112 for storing fuel that issupplied to the fuel rail 108. More particularly, a fuel pump 114 may beoperable by controller 128 to pump fuel from the fuel tank 112 to thefuel rail 108. In the illustrated embodiment, the fuel pump 114 is shownoutside of the fuel tank 112 positioned downstream of the fuel tank andupstream of the fuel rail 108. In some embodiments, the fuel pump 114may be positioned inside the fuel tank 112 in what is known as anin-tank fuel pump. The fuel tank 112 may be pressurized to maintain fuelstored in the fuel tank at a desired pressure. For example, the fueltank may be pressurized at a pressure suitable to store propane in aliquefied state. The fuel pump may pump liquefied propane from the fueltank to the fuel rail. Moreover, the pressure at which the fuel systemoperates may change according to the type of fuel (e.g., liquid propane,gaseous propane, gasoline, etc.) that is stored in the fuel system.

A delivery check valve 116 may be positioned downstream of the fuel pump114 to force fuel pumped from the fuel pump at a predetermined pressureto the fuel rail 108 so that fuel does not return along the same path tothe fuel pump. A first solenoid valve 118 may be positioned downstreamof delivery check valve 116 to control the flow of fuel to fuel rail 108or from the fuel rail to a return line 119. It will be appreciated thatthe fuel return line may be positioned in any suitable portion of thefuel system. For example, the return line can be positioned inside or atthe fuel tank. As another example, the fuel return line can bepositioned near the entry/exit to the fuel rail. The difference inposition can affect the time to re-pressurize the fuel system. Forexample, if the return line runs all the way to the fuel rail, the timeto re-pressurize the fuel system may be reduced and/or substantiallyminimized.

In some embodiments, fuel system 110 may be what is known as amulti-fuel system that selectively provides a plurality of differenttypes of fuel to the fuel rail 108 based on the mode of operation. As anexample, the fuel system may be a bi-fuel system that selectivelyprovides gasoline and/or liquid propane to the fuel rail based on themode of operation.

A three-way valve 120 may be positioned upstream of the fuel rail 108and downstream of the first solenoid valve 118 and the return line 119to selectively control the flow of a desired type of fuel to the fuelrail 108. The state of the three-way valve 120 may be controlled bycontroller 128 to vary which type of fuel is delivered to the fuel rail108. In embodiments of the fuel system 110 where only one type of fuelis delivered to the fuel rail 108, the three-way valve 120 may beomitted.

Fuel in the fuel rail 108 may be returned to the fuel tank 112 via thereturn line 119. An ejector 124 (a.k.a. eductor, jet pump, venturi pump,aspirator) may be positioned in the return line 119 to provide a singlefuel rail evacuation stage. The ejector 124 pumps fuel in return line119 to fuel tank 112 based on receiving a motive flow from the fuel pump114. The fuel pump 114 is operable to provide a motive flow to theejector 124 via a motive flow line 121 that is positioned downstream ofthe fuel pump and upstream of the delivery check valve 116. Moreparticularly, the ejector 124 converts flow energy of a motive fluid(e.g., fuel from the fuel pump) to create a low pressure zone that drawsin and entrains a suction fluid (e.g., fuel in the return line) thatenters an inlet of the ejector from the return line 119. Inside theejector 124, a mix of the motive fluid and the suction fluid expands andthe velocity is reduced which results in recompressing the mix of fluidsby converting velocity back into pressure energy that pumps the fuelthrough an outlet of the ejector 124 to fuel tank 112.

A return check valve 122 is positioned in the return line 119 downstreamof the ejector 124 to force fuel returning from the fuel rail 108 at apredetermined pressure to ejector 124 so that fuel is evacuated from thefuel rail 108. In some embodiments, the fuel rail may have a single fuelport. In some embodiments, the fuel rail may have a dedicated port forfuel entry and a dedicated port for fuel exit. In such embodiments, thefuel exit port can be located at a low point in the fuel rail so thatthe liquid fuel is first evacuated before gaseous fuel is evacuated. Inthis way, the time to empty the fuel rail can be reduced. Note that someliquid fuel rails typically feed from the top to minimize the risk of“fuel push out” due to the fuel's vapor pressure. In the systemdescribed herein, the feed may be positioned at a low point so that thefuel's vapor pressure enhances fuel push-out to more quickly evacuatethe fuel rail.

A second solenoid valve 126 is positioned upstream of the outlet of theejector 124 and downstream of the fuel tank 112. The state of the firstsolenoid valve 118 and the state of the second solenoid valve 126 (andthe three-way valve 120 when applicable) may be controlled by controller128 to pressurize the fuel rail 108 or evacuate the fuel rail based onthe mode of operation. For example, during a fuel rail pressurizationmode where the engine is operating, the controller can open the firstsolenoid valve 118 and close the second solenoid valve 126 (and adjustthe three-way valve so that a first type of fuel stored in fuel tank 112is allowed to flow to the fuel rail in a multi-fuel system) to directfuel pumped from the fuel pump 114 to the fuel rail 108 to pressurizethe fuel rail. As another example, during a fuel rail evacuation modewhen the engine is shut-off or not operating, the controller 128 canclose the first solenoid valve 118 and open the second solenoid valve126 (and adjust the three-way valve so that fuel in the fuel rail 108 isallowed to flow from the fuel rail to the return line 119 in amulti-fuel system) to direct fuel pumped from the ejector 124 back tothe fuel tank 112.

It will be appreciated that the engine system may operate in the fuelrail evacuation mode until a suitable amount of fuel has been evacuatedfrom the fuel rail or until a suitable fuel rail pressure has beenachieved. At which time (e.g., a predetermined duration after engineshut-off), the fuel pump may be shut-off and the state of the solenoidvalves may be varied since the fuel pump is not operating to increasethe pressure in the fuel system.

In some embodiments, the solenoid valves 118 and 126 can be replacedwith a three-way valve where the flow can be selectively placed innormal pumping mode during vehicle/engine in-use conditions or set tocirculate flow through the ejector to evacuate the fuel rail duringvehicle/engine shut-off conditions. Note the solenoid valves, checkvalves, and three-way valve are exemplary. It will be appreciated thatany suitable type of valve may be implemented in the fuel system. Insome embodiments, one or more valve may be omitted from the fuel system.

The controller 128 is shown receiving various signals from sensors 132coupled to engine 102 and fuel system 110. The sensors 132 may measureor derive any suitable parameter that is considered to control operationof the engine 102 and/or the fuel system 110. For example, the sensors132 may measure pressure, temperature, engine speed, etc. The controller128 may adjust operation of actuators 130 coupled to engine 102 and fuelsystem 110 in order to control different modes of operation. Forexample, the actuators 130 may include fuel system valves, enginevalves, the fuel pump, etc. The controller 128 may include a storagemedium, such as read-only memory, that can be programmed with computerreadable data representing instructions executable by a processor of thecontroller for performing the methods described below as well as othervariants that are anticipated but not specifically listed.

By implementing the above described engine system in a vehicleapplication that employs liquid propane for combustion, a variety ofpotential benefits may be achieved. For example, due to the density ofliquid propane relative to gaseous propane, the ability to evacuate thefuel rail after engine shut-off may provide a much greater reduction inemissions and increase in fuel economy relative to a gaseous propaneapplication. Further, by employing an ejector that is operable based ona motive flow from a fuel pump that is already implemented in the fuelsystem, the fuel rail can be evacuated without the expense of anadditional mechanical vacuum pump. Moreover, unlike a mechanical pump,the ejector is able to handle the phase change of liquid/gas beingevacuated. Thus, even if propane undergoes a phase change duringevacuation, the propane can still be pumped back to the fuel tank.Additionally, the ejector operates in a simple manner with no movingparts.

FIG. 2 schematically shows an embodiment of an engine system where afuel system 200 includes a plurality of fuel rail evacuation stages.Each of the fuel rail evacuation stages includes an ejector thatreceives a motive flow from the fuel pump during an engine shut-offcondition to evacuate the fuel rail. The motive flow of the ejectors isconnected in parallel. The suction flow of the ejectors is connected inseries so that the output of one ejector is fed to the input of anotherejector which allows a lower pressure in the fuel rail to be obtainedfor a greater amount of fuel to be evacuated.

A first evacuation stage includes an ejector 125 which is positioned inthe return line 119 upstream of a check valve 123. The ejector 125receives a motive flow from the fuel pump 114 via motive flow line 121.Fuel is pumped into an inlet of the ejector 125 from the return line 119to lower the pressure of the fuel rail from a first pressure level to asecond pressure level. Fuel pumped from an outlet of the ejector 125travels to a second evacuation stage and enters an inlet of the ejector124. Fuel is pumped through the ejector 124 to lower the pressure of thefuel rail from the second pressure level to a third pressure level. Fuelpumped from an outlet of the ejector 124 is returned to the fuel tank112 for storage.

A check valve 122 is positioned in the return line 119 in between theoutlet of the ejector 125 and the inlet of the ejector 124. The checkvalve 122 may be set at a different actuation pressure than check valve123 so that fuel may be pumped through the first fuel rail evacuationstage before the second stage is activated. That is, the check valve 122and the check valve 123 work in conjunction to allow the ejector 125 todo all the pumping work in the first evacuation stage to lower the fuelrail pressure from the first pressure level to the second pressure levelbefore the ejector 124 in the second evacuation stage becomes operableto lower the fuel rail pressure from the second pressure level to thethird pressure level. The plurality of evacuation stages and, moreparticularly, this check valve configuration evacuates the fuel railsooner than would be possible with only a single check valve positionedin the return line. Correspondingly, the fuel pump may be shut-offsooner after engine shut-off to reduce operating noise.

In another embodiment, ejectors may be staged so that the motive flow isconnected in series. In such a configuration, any given ejector may havea performance line that trades off vacuum at zero flow rate with flowrate at zero vacuum. Series staging allows the high flow rate/low vacuumstage to work first and then the low flow rate/high vacuum stage to comeinto effect later.

FIG. 3 schematically shows an embodiment of an engine system where afuel system 300 selectively provides a plurality of different types offuel to the fuel rail. Furthermore, the fuel system 300 includes a fuelrail evacuation stage to evacuate fuel that is in the fuel rail uponengine shut-off. The fuel system 300 shares a similar configuration asthe fuel system 110 shown in FIG. 1 and described above. Specifically,the fuel system 300 includes a first fuel stage that includes a fueltank 112 to store a first type of fuel, a fuel pump 114 selectivelyoperable to pump fuel from the fuel tank 112. The fuel system 300includes an ejector 124 positioned in a fuel return line 119. During afuel rail pressurization mode, a first solenoid valve 118 positioneddownstream of the fuel pump 114 and a second solenoid valve 126positioned upstream of the ejector 124 can be cooperatively controlledby controller 128 to direct fuel to the fuel rail 108 for injection tocylinders 104 via fuel injectors 106 based on a state of three-way valve120. During a fuel rail evacuation mode, the first solenoid valve 118and the second solenoid valve 126 can be cooperatively controlled bycontroller 128 to direct fuel from the fuel pump 114 to the ejector 124via motive flow line 121 to create a motive flow in the ejector to pumpfuel from the fuel rail 108 to the fuel tank 112.

Furthermore, the fuel system includes a second fuel stage including afuel tank 134 to store a second type of fuel different from the fueltype stored in fuel tank 112, a fuel pump 136 selectively operable topump fuel from the fuel tank 134 to the fuel rail 108 based on the stateof three-way valve 120. In some embodiments, the fuel pump 136 may bepositioned in the fuel tank 134 in what as known as an in-tank fuelpump. A delivery check valve 138 is positioned downstream of the fuelpump 136 and upstream of the three-way valve 120. The delivery checkvalve 138 inhibits fuel pumped from the fuel pump 136 from returningalong the same path back to the fuel pump. The second fuel stageincludes a return line 140. A return check valve 142 is positioned inthe return line 140 downstream of the fuel tank 134 to force excess fuelfrom the fuel rail 108 at a predetermined pressure to return to the fueltank 134.

During the fuel rail pressurization mode, one or more of the first typeof fuel and the second type of fuel can be provided to the fuel railbased on the state of the three-way valve 120 as controlled by thecontroller 128. Further during the fuel rail evacuation mode, the stateof the three-way valve 120 is set by the controller 128 so that whatevertype of fuel that resides in the fuel rail is directed to the first fuelstage and pumped to the fuel tank 112 via the ejector 124. It will beappreciated that evacuation of the fuel rail allows for the fuel type tobe selected upon engine start because the fuel rail will besubstantially empty with only some residual fuel vapor from the previousengine shutdown. By selecting the fuel type at engine start combustioncan be made more stable since the characteristics of the fuel type canbe known. Moreover, the ability to select a fuel type at engine startcan be beneficial for stabilizing combustion in various environmentalconditions.

As an example, the multi-fuel system may be implemented in a vehiclethat selectively combusts liquid propane and/or gasoline. Accordingly,liquid propane may be stored in the first fuel stage and gasoline may bestored in the second fuel stage. At engine start, the controller mayoperate in the fuel rail pressurization mode and selects the type offuel to be delivered to the fuel rail based on operating conditions. Forexample, at lower temperatures liquid propane may be selected at enginestart to provide increased dispersion for more stable combustion. Asanother example, at higher temperatures gasoline may be selected atengine start to provide increased charge cooling of the cylinders.

Furthermore, upon engine shut-off, the controller may operate in thefuel rail evacuation mode and operates the fuel pump in the first stageto provide the motive flow to the ejector to pump whatever fuel is inthe fuel rail to the fuel tank in the first fuel stage. In some cases,gasoline may be pumped into the fuel tank that stores the liquidpropane. However, the amount of fuel in the fuel rail compared to theamount of fuel in the fuel tank is relatively small and has littleeffect on the composition of the fuel in the fuel tank.

Note in some embodiments, the fuel system 300 may be modified to includea plurality of fuel rail evacuation stages to evacuate fuel from thefuel rail upon engine shut-off in a quicker manner than would bepossible with only a single fuel rail evacuation stage.

FIG. 4 schematically shows a fuel system 400 where fuel flow can becontrolled to evacuate liquid fuel and gaseous fuel from a fuel railduring a vehicle shut-off condition. During fuel rail evacuation, thefuel system 400 is operable in a first mode where liquid fuel isevacuated from the fuel rail 108. The evacuated liquid fuel may bedirected from the fuel rail 108 to the fuel tank 112. In particular,during the first mode valve 120 can be closed by controller 128 toprevent fuel from flowing back to the fuel pump 114 (or to another fuelsystem where applicable) and valve 127 can be opened by controller 128to create a path in return line 119 from the fuel rail 108 to the fueltank 112. The liquid fuel can be “pushed out” of the fuel tank based ona pressure difference between the fuel rail 108 and the fuel tank 112.For example, upon vehicle shut-off the fuel tank can to be much coolerthan the fuel rail, as such, the fuel pressure in the fuel rail is muchhigher than the fuel pressure in the fuel tank. Since the pressure inthe fuel tank is much lower, the liquid fuel can be drained from thefuel rail. In other words, the first mode of operation can be performedwhen the fuel rail pressure is higher than the fuel tank pressure.

Furthermore, as the liquid fuel drains from the fuel rail the remaininggaseous fuel expands to aid in pushing the liquid fuel from the fuelrail more quickly. The return line 119 and the fuel rail 108 can bedesigned to promote drainage of the liquid fuel. In particular, thereturn line 119 can be coupled to a lower or bottom portion of the fuelrail 108 to allow the more dense liquid fuel to be evacuated ahead ofthe gaseous fuel.

The expansion of gaseous fuel in the fuel rail causes the fuel railpressure to drop which can inhibit the fuel from evacuating to the fueltank. The drop in pressure can be measured by fuel rail pressure sensor156, which can be one of a plurality of sensors 132 that measure engineand/or fuel system conditions. In response to the fuel rail pressuredropping below a threshold, the fuel system can transition out of thefirst mode of operation and valve 127 can be closed by controller 128.In one example, the threshold is a pressure level at which fuel in thefuel rail changes phase from liquid fuel to gaseous fuel or the criticalpoint. In some cases, the threshold can be set to a pressure level belowthe critical point of the fuel.

Next, the fuel system can operate in the second mode to evacuate gaseousfuel from the fuel rail. In particular, a valve 144 located in anevaporation line 145 positioned between the fuel rail 108 and a fuelvapor canister 146 can be opened by the controller 128 so that gaseousfuel can migrate out of the fuel rail to the fuel vapor canister. Insome embodiments, opening of the valve 144 can be delayed a suitabletime after closing the valve 127 so as to permit the fuel railtemperature to increase so that the remaining fuel evaporates.

The fuel rail 108 can be designed to aid in migration of gaseous fuelfrom the fuel rail to the fuel vapor canister 146. In particular, theevaporation line can be coupled to an upper or top portion of the fuelrail so that the gaseous fuel can easily enter the evaporation line 145.As such, the evaporation line 145 can be coupled to the fuel rail at aposition that is higher than a position that the return line 119 iscoupled to the fuel rail.

Fuel that is stored in the fuel vapor canister 146 can be supplied to anintake manifold (not shown) of engine 102 during subsequent operationvia supply line 147 when valve 148 is opened by controller 128. Undersome conditions such as to relieve pressure, fuel may be vented from thefuel vapor canister 146 to the atmosphere by opening valve 150. In someembodiments, the fuel rail can be evacuated by merely applying the pushout conditions to drain the liquid fuel and the evaporation conditionsto evacuate the gaseous fuel without use of a vacuum pump or acompressor.

Note the fuel system 400 may incorporate multi-fuel elements asdescribed above because the fuel system has the ability to providedifferent fuels to the engine for combustion since the fuel rail isevacuated at vehicle shut-off.

FIG. 5 schematically shows a fuel system 500 where fuel flow can becontrolled to regulate a temperature of a high pressure fuel pump sothat fuel enters the high pressure fuel pump in a liquid state. Liquidfuel can be pumped from fuel tank 112 by an in-tank or low pressure fuelpump 114 to a high pressure fuel pump 152. The high pressure fuel pumpcan pump the liquid fuel to a higher pressure that is suitable fordirect injection by fuel injectors 106.

A temperature sensor 154 monitors the temperature of the high pressurefuel pump 152. If the temperature of the high pressure fuel pump 152becomes greater than a threshold, at least some liquid fuel can bedirected to an expansion section 158 that is located in return line 119.The threshold may be any suitable temperature where a correspondingpressure is lower than the phase change pressure or critical point ofthe fuel. In particular, valve 127 opens to direct liquid fuel to theexpansion section 158. In some embodiments, valve 127 may be athermostatic valve that opens in response to reaching a predeterminedtemperature. In some embodiments, valve 127 may be a solenoid valve thatcan be opened by controller 128 in response to receiving a temperaturefrom temperature sensor 154 that is at or above the threshold.

The expansion section 158 can be thermally connected to the highpressure fuel pump 152 so that when liquid fuel is fed to the expansionsection and expands into a gaseous state a temperature drop is createdthat provides cooling to the high pressure fuel pump 152 andcorrespondingly to fuel entering the fuel pump.

After the fuel expands to a gaseous state in the expansion section 158of return line 119, the gaseous fuel can be directed differently basedon fuel system configurations and/or conditions. In some embodiments,the fuel system 500 may include an evaporation line 163 that ispositioned between the fuel vapor canister 146 and the fuel return line119 downstream of the expansion section 158. A valve 164 located in theevaporation line 163 can be opened and valve 160 can be closed bycontroller 128 to direct the gaseous fuel from the return line 119 tothe fuel vapor canister 146. In some embodiments, the gaseous fuel mayexit the expansion section 158 and valve 160 can be opened and valve 164can be closed to return the fuel to the fuel tank 112.

Note the fuel system 500 may incorporate multi-fuel elements asdescribed above because the fuel system has the ability to regulate thetemperature of the fuel pump to accommodate different fuels havingdifferent critical points so that fuel entering the fuel pump remains ina liquid state.

The configurations illustrated above enable various methods fordistributing fuel in a fuel system of a motor vehicle. Accordingly, somesuch methods are now described, by way of example, with continuedreference to above configurations. It will be understood, however, thatthese methods, and others fully within the scope of the presentdescription, may be enabled via other configurations as well.

It will be understood that the example control and estimation routinesdisclosed herein may be used with various system configurations. Theseroutines may represent one or more different processing strategies suchas event-driven, interrupt-driven, multi-tasking, multi-threading, andthe like. As such, the disclosed process steps (operations, functions,and/or acts) may represent code to be programmed into computer readablestorage medium in the controller.

FIG. 6 shows an embodiment of a method 600 for controlling a fuel systemincluding one or more fuel rail evacuation stages. The method 600 may beperformed by controller 128. At 602, the method may include determiningoperating conditions. Operating conditions may be determined by thecontroller 128 based on signals received from sensors 132. Exampleoperating conditions include various temperatures (e.g., fuel pump, fuelrail, ambient air, engine, fuel system, etc.), various pressures (e.g.,fuel rail fuel pump, fuel tank, fuel system, etc.), state of the engine,etc.

At 604, the method may include determining if the vehicle is in-use.This determination may include determining if the engine 102 is startingand/or operating. As another example, the determination may includedetermining if the vehicle is moving. If it is determined that vehicleis in-use the method moves to 606. Otherwise, the method returns to 604.

At 606, the method may include operating in the fuel rail pressurizationmode. Operating in the fuel rail pressurization mode may include, at608, opening the solenoid valve 118 positioned downstream of the fuelpump 114 and upstream of the fuel rail 108, at 610, closing the solenoidvalve 126 positioned upstream of the ejector 124 and downstream of thefuel tank 112, and, at 412, operating the fuel pump 114 to deliver fuelfrom the fuel tank to the fuel rail.

At 614, the method may include determining if the vehicle is shut-off.This determination may include determining if the vehicle is turned off.In some embodiments, the engine may be shut-off but the vehicle stillmay be in-use, such as a hybrid vehicle operating in an electric mode.Under some conditions, the engine may be stopped and restartedrepeatedly in a short period, and thus it may not be desirable toevacuate the fuel rail. As such, it may be desirable to determinewhether or not to evacuate the fuel rail based on more factors than justthe state of the engine. If it is determined that the vehicle isshut-off the method moves to 616. Otherwise, the method returns to 606.

At 616, it is determined that the vehicle is shut-off and the method mayinclude operating in the fuel rail evacuation mode. Operating in thefuel evacuation mode may include at 418, closing the solenoid valve 118,at 620, opening the solenoid valve 126, and at 622, operating the fuelpump 114 to provide the motive flow to the ejector 124 to pump fuel fromthe fuel rail to the fuel tank 112.

At 624, the method may include determining if the fuel rail 108 has beenevacuated. This determination may include determining if a predeterminedevacuation time has elapsed or determining if the fuel rail has beenevacuated in any other suitable manner including reading a fuel railpressure sensor. For example, the fuel rail can be evacuated till a fuelrail pressure is lower than the fuel's vapor pressure at the presenttemperature, which results in all the liquid fuel being extracted fromthe fuel rail. Note that the fuel rail need not be evacuated to thispressure level to have a beneficial effect and evacuation may beperformed to lower the fuel rail pressure till to any suitable pressurelevel is achieved. If it is determined that the fuel rail 108 has beenevacuated the method moves to 626. Otherwise, the method returns to 624.

At 626, the method may include shutting off the fuel pump since asuitable amount of fuel has been evacuated from the fuel rail 108 or afuel rail pressure has achieved a suitable pressure level. After thefuel pump is shut-off the method returns to other operation.

By operating in the fuel rail pressurization mode when the vehicle isin-use, fuel may be delivered to the fuel rail for injection andcombustion in the engine. Furthermore, by operating in the fuel railevacuation mode when the engine is shut-off, fuel from the fuel pump mayprovide the motive flow to the ejector to pump fuel from the fuel railto the fuel tank. In this way, evaporative emissions associated withfuel evaporating and leaking out of the fuel rail via the fuel injectorsmay be reduced.

FIG. 7 shows an embodiment of a method 700 for controlling a multi-fuelsystem including one or more fuel rail evacuation stages. The method 700may be performed by controller 128. At 702, the method may includedetermining operating conditions. At 704, the method may includedetermining if the vehicle is in-use. If it is determined that vehicleis in-use the method moves to 706. Otherwise, the method returns to 704.

At 706, the method may include operating in the fuel rail pressurizationmode. At 708, the method may include determining if a first fuel from afirst fuel stage or a second fuel from a second fuel is selected fordelivery to the fuel rail 108. If the first fuel is selected, operatingin the fuel rail pressurization mode may include, at 710, switching thethree-way valve 120 to the first fuel stage, at 712, opening thesolenoid valve 118 positioned downstream of the fuel pump 114 andupstream of the fuel rail 108, at 714, closing the solenoid valve 126positioned upstream of the ejector 124 and downstream of the fuel tank112, and, at 716, operating the fuel pump 114 to deliver the first fuelfrom the fuel tank to the fuel rail. If the second fuel is selected,operating in the fuel rail pressurization mode may include, at 718,switching the three-way valve 120 to the second fuel stage, and, at 720,operating the fuel pump 136 to deliver the second fuel from the fueltank 134 to the fuel rail 108.

At 722, the method may include determining if the vehicle is shut-off.If it is determined that the vehicle is shut-off the method moves to724. Otherwise, the method returns to 706.

At 724, it is determined that the vehicle is shut-off and the method mayinclude operating in the fuel rail evacuation mode. Operating in thefuel evacuation mode may include at 726, switching the three-way valve120 to the first fuel stage, at 728, closing the solenoid valve 118, at730, opening the solenoid valve 126, at 732, shutting off the fuel pump136, and at 734, operating the fuel pump 114 to provide the motive flowto the ejector 124 to pump fuel from the fuel rail 108 to the fuel tank112.

At 736, the method may include determining if the fuel rail 108 has beenevacuated. If it is determined that the fuel rail 108 has been evacuatedthe method moves to 738. Otherwise, the method returns to 724.

At 738, the method may include shutting off the fuel pump 114 since asuitable amount of fuel has been evacuated from the fuel rail 108 or afuel rail pressure has achieved a suitable pressure level. After thefuel pump 114 is shut-off the method returns to other operation.

By operating in the fuel rail pressurization mode when the vehicle isin-use, a selected fuel may be delivered to the fuel rail for injectionand combustion in the engine. Furthermore, by operating in the fuel railevacuation mode when the engine is shut-off, fuel from the fuel pump inthe first fuel stage may provide the motive flow to the ejector to pumpfuel from the fuel rail to the fuel tank. In this way, evaporativeemissions associated with fuel evaporating and leaking out of the fuelrail via the fuel injectors may be reduced. Moreover, since fuel thefuel rail is evacuated at engine shut-off, a fuel type may be selectedfor injection at engine start. In this way, combustion can be adjustedin a multi-fuel system to accommodate operating conditions.

FIG. 8 shows an embodiment of a method 800 for controlling a fuel systemto evacuate fuel from a fuel rail. The method 800 may be performed bycontroller 128. At 802, the method may include determining operatingconditions. At 804, the method may include determining if the vehicle isin-use. If it is determined that vehicle is in-use the method moves to806. Otherwise, the method returns to 804.

At 806, the method may include operating in a fuel rail liquid fuelevacuation mode. Operating in the fuel rail liquid fuel evacuation modemay include, at 808, closing the solenoid valve 120 positioned betweenthe fuel pump 114 and the fuel rail 108 so that fuel does flow back tothe fuel pump, and at 810, opening the solenoid valve 127 positioned inthe return line 119 between the fuel rail 108 and the fuel tank 112 todeliver liquid fuel from the fuel tank to the fuel rail. Due to thedifference in pressure between the fuel rail and the fuel tank atvehicle shut-off, the liquid fuel can be pushed out of the fuel rail sothat it drains to the fuel tank.

At 812, the method may include determining if the fuel rail pressure isgreater than a threshold. As an example, the threshold may be a pressurelevel at which the liquid fuel changes to a gaseous state or thecritical point of the fuel. As another example, the threshold may be apressure level lower than the critical point of the fuel. If the fuelrail pressure is greater than the threshold, the method returns to 806.Otherwise, the method moves to 814.

At 814, the method may include operating in a fuel rail gaseous fuelevacuation mode. Operation in the fuel rail gaseous fuel evacuation modemay include at 816, closing solenoid valve 127 between the fuel rail 108and the fuel tank 112, and, at 818, opening the solenoid valve 144between the fuel rail 108 and the fuel vapor canister 146. In someembodiments, where the fuel system includes a check valve positionedbetween the fuel rail and the fuel vapor canister, the solenoid valvemay be opened in response to transitioning out of the fuel rail liquidfuel evacuation mode, and gaseous fuel may flow to the fuel vaporcanister once the fuel rail pressure has increased enough to actuate thecheck valve. In other embodiments, opening of solenoid valve 144 may bedelay an amount of time suitable enough for fuel remaining in the fuelrail to evaporate. Once the solenoid valve 144 is open the gaseous fuelcan migrate from the fuel rail 108 and be absorbed by the fuel vaporcanister 146.

At 820, the method may include determining if the vehicle is in-use. Asone example, the determination is made based on engine start-up. If itis determined that the vehicle is in-use, the method moves to 822.Otherwise, the method returns to 814.

At 822, the method may include closing the solenoid valve 144 to preventfuel injected into the fuel rail from venting to the fuel vaporcanister.

At 824, the method may include opening the solenoid valve 148 positionedbetween the fuel vapor canister and an intake of the engine to evacuatefuel from the fuel vapor canister for combustion in the engine.

By evacuating liquid fuel to the fuel tank and gaseous fuel to the fuelvapor canister, the fuel rail can be evacuated in order to reduceevaporative emissions from the fuel rail. Furthermore, by evacuating thefuel rail, the fuel system has the ability to provide one of a pluralityof different types of fuels at the next start-up since the fuel rail issubstantially empty. In this way, combustion can be adjusted in amulti-fuel system to accommodate operating conditions.

FIG. 9 shows an embodiment of a method 900 for controlling a fuel systemto regulate a temperature of a fuel pump to permit liquid to fuel enterthe fuel pump. The method 900 may be performed by controller 128. At902, the method may include determining operating conditions. At 904,the method may include determining if a fuel pump temperature is greaterthan a threshold. As an example, the threshold may be a temperaturecorresponding to a pressure at which the fuel changes from a liquidstate to a gaseous state or the critical point of the fuel. As anotherexample, the threshold may be a temperature corresponding to a pressurethat is lower than the critical point of the fuel. If it is determinedthat the fuel pump temperature is greater than the threshold the methodmoves to 906. Otherwise, the method returns to 904.

At 906, the method may include opening the solenoid valve 127 positionedbetween the fuel pump 152 and the expansion section 158. Once thesolenoid valve 127 is open, at least some liquid fuel pumped from fuelpump 114 is directed to the expansion section 127 where it expands to agaseous state and creates a drop in temperature that is thermallytransferred to the fuel pump 152 to cool the fuel pump.

At 908, the method may include distributing gaseous fuel in the returnline 119. Under some conditions, at 910, the method may include openingthe solenoid valve 160 positioned downstream of the expansion section158 in the return line 119 and closing valve 164 to direct gaseous fuelfrom the expansion section to the fuel tank. Under some conditions, at912, the method may include opening the solenoid valve 164 positionedbetween the fuel vapor canister 146 and the expansion section 158 andclosing valve 160 to direct gaseous fuel from the expansion section tothe fuel vapor canister.

At 914, the method may include determining if the fuel pump temperatureis greater than a second threshold that is lower than the firstthreshold. If the fuel pump temperature is greater than the secondthreshold the method returns to 906. Otherwise, the method moves to 916.

At 916, the method may include closing the solenoid valve 127 to stopdirecting fuel to the expansion section 158 since the fuel pump 152 doesnot require cooling to permit liquid fuel to enter the fuel pump.

By directing liquid fuel to the expansion section, the liquid fuel canbe used as a refrigerant to cool the fuel pump so that the liquid fueldoes not reach the liquid-to-gas phase change pressure. In this way, thefuel pump temperature can be controlled so as to inhibit gaseous propanefrom entering the fuel pump and inhibiting fuel pump operation.Moreover, regulating the temperature of the fuel pump in this manner maypermit the fuel pump to pump different types of fuel for combustion. Inthis way, combustion can be adjusted in a multi-fuel system toaccommodate operating conditions.

It will be understood that some of the process steps described and/orillustrated herein may in some embodiments be omitted without departingfrom the scope of this description. Likewise, the indicated sequence ofthe process steps may not always be required to achieve the intendedresults, but is provided for ease of illustration and description. Oneor more of the illustrated actions, functions, or operations may beperformed repeatedly, depending on the particular strategy being used.

Finally, it will be understood that the articles, systems and methodsdescribed herein are exemplary in nature, and that these specificembodiments or examples are not to be considered in a limiting sense,because numerous variations are contemplated. Accordingly, the presentdescription includes all novel and non-obvious combinations andsub-combinations of the various systems and methods disclosed herein, aswell as any and all equivalents thereof. For example, methods mayinclude delivering different fuel types to the engine via the same fuelrail under different operating conditions, where fuel flow isselectively directed through an ejector to evacuate the fuel rail of aspecific type of fuel so that the rail may be filled and pressurizedwith a different fuel type. The evacuation may occur during engineshutdown, engine rest, engine off, (any of which may be during vehiclerunning (hybrid-vehicle) conditions), and/or vehicle off/shutdownconditions.

1. A method for controlling fuel flow in a vehicle comprising: during avehicle shut-off condition: during a first mode of operation, directingliquid fuel from a fuel rail to a fuel tank until fuel rail pressurebecomes less than a threshold; and then during a second mode ofoperation, directing gaseous fuel from the fuel rail to a fuel vaporcanister, the fuel vapor canister positioned external to the fuel tank.2. The method of claim 1, further comprising: after transitioning out ofthe first mode in response to the fuel rail pressure becoming less thanthe threshold, operating in the second mode.
 3. The method of claim 1,wherein the threshold is a pressure level at which fuel in the fuel railchanges phase from liquid fuel to gaseous fuel.
 4. The method of claim1, further comprising: after transitioning out of the second mode,directing a different fuel type to the fuel rail.
 5. The method of claim1, wherein directing fuel from the fuel rail to the fuel tank includesopening a first valve located in a return line positioned between thefuel rail and the fuel tank.
 6. The method of claim 5, wherein directingfuel from the fuel rail to the fuel vapor canister includes closing thefirst valve and opening a second valve located in an evaporation linepositioned between the fuel rail and the fuel vapor canister.
 7. Themethod of claim 1, wherein a fuel type in the fuel rail includes liquidpropane and the fuel rail is evacuated without use of a vacuum pump or acompressor.
 8. A system for controlling fuel flow in a vehicle,comprising: a fuel tank; a fuel rail positioned downstream of the fueltank; a fuel return line positioned downstream of the fuel tank andupstream of the fuel rail; a first valve located in the return linebetween the fuel rail and the fuel tank; a fuel vapor canisterpositioned external to the fuel tank; an evaporation line positionedbetween the fuel rail and the fuel vapor canister; a second valvepositioned in the evaporation line between the fuel rail and the fuelvapor canister; and a controller for, during a first mode, opening thefirst valve and closing the second valve to direct liquid fuel from thefuel rail to the fuel tank until fuel rail pressure becomes less than athreshold, and then during a second mode, closing the first valve andopening the second valve to direct gaseous fuel from the fuel rail tothe fuel vapor canister, wherein the controller operates in the firstand second modes during a vehicle shut-off condition.
 9. The system ofclaim 8, wherein the return line couples to the fuel rail at a firstposition and the evaporation line couples to the fuel rail at a secondposition that is located higher than the first position.
 10. The systemof claim 8, wherein after transitioning out of the first mode, thecontroller operates in the second mode.
 11. The system of claim 10,wherein the threshold is a pressure level at which fuel in the fuel railchanges phase from liquid fuel to gaseous fuel.
 12. The system of claim11, wherein a type of fuel in the fuel rail includes liquid propane andthe threshold is a pressure level at which liquid propane transitions togaseous fuel.
 13. The system of claim 8, further comprising: a secondfuel tank for storing a second fuel type; a second fuel pump to pumpfuel from the second fuel tank; a fourth valve positioned between thesecond fuel pump and the fuel rail; and the controller, after operatingin the second mode, opening the fourth valve and operating the secondfuel pump to direct the second fuel type to the fuel rail.
 14. A systemfor controlling fuel flow in a vehicle, comprising: a fuel tank; a fuelpump operable to pump fuel from the fuel tank; a fuel rail positioneddownstream of the fuel pump; a fuel return line positioned between thefuel tank and the fuel rail; a first valve located in the return linebetween the fuel rail and the fuel tank; a fuel vapor canisterpositioned external to the fuel tank; an evaporation line positionedbetween the fuel rail and the fuel vapor canister; a second valvepositioned in the evaporation line between the fuel rail and the fuelvapor canister; a third valve positioned between the fuel pump and thefuel rail; and a controller for, in a fuel rail evacuation mode during avehicle shut-off condition, opening the first valve, closing the secondvalve, and closing the third valve to direct liquid fuel from the fuelrail to the fuel tank when a fuel rail pressure is greater than athreshold pressure level at which fuel in the fuel rail transitions fromliquid fuel to gaseous fuel, and closing the first valve, opening thesecond valve, and closing the third valve to direct gaseous fuel fromthe fuel rail to the fuel vapor canister after the fuel rail pressurehas dropped below the threshold pressure level to thereby evacuate fuelfrom the fuel rail.
 15. The system of claim 14, wherein a fuel type inthe fuel rail includes liquid propane and the fuel rail is evacuatedwithout use of a vacuum pump or a compressor.
 16. The system of claim14, wherein the return line couples to the fuel rail at a first positionand the evaporation line couples to the fuel rail at a second positionthat is located higher than the first position.
 17. The system of claim14, further comprising: a second fuel tank for storing a second fueltype; a second fuel pump to pump fuel from the second fuel tank; afourth valve positioned between the second fuel pump and the fuel rail;and the controller, after operating in the second mode, opening thefourth valve and operating the second fuel pump to direct the secondfuel type to the fuel rail.